1. Field of the Invention
The present invention generally relates to wellhead components for supporting the use of downhole pumps. More particularly, the present invention relates to a top mounted rotating stuffing box configured for sealing production fluid from the atmosphere.
2. Description of the Related Art
Oil and gas in newly discovered reservoirs usually flow to the surface by natural lift. The natural formation pressure of a reservoir provides the energy or driving force to move reservoir fluids horizontally into a wellbore, through production tubing, and through surface processing equipment. During the life of any producing well, however, the natural reservoir pressure decreases as reservoir fluids are removed from the formation. As the natural downhole pressure drops to the sum of the hydrostatic head in the wellbore and the facility pressure, the fluids cease to spontaneously flow to the surface. Therefore, artificial lift methods such as sucker-rod pumping, downhole pumping, and gas injection lift techniques, for example, are employed to lift the fluids to the surface.
Many wells today use a downhole pumping apparatus such as progressing cavity pump (PCP) systems to lift fluids from within the production well to the surface. As its name implies, a PCP system comprises a PCP, also referred to herein as “pump”, located within the wellbore and a drive system located at the surface of the well. A drive system comprises, among other components, a motor (typically a hydraulic motor) for providing torque and rotation to a drive string, and a drive unit for transmitting the torque downhole. A drive string disposed within the production tubing connects the pump and hydraulic motor. The pump comprises a rotor disposed within a stator located within the production tubing. The well is produced by utilizing the hydraulic motor to rotate the drive string, which, in turn, drives the rotor of the pump. The result is a non-pulsating positive displacement flow of fluids towards the surface of the well.
A major problem associated with downhole PCP implementations is sealing the pressurized production fluid and preventing it from escaping into the atmosphere from surface equipment. Often, stuffing boxes are used to help seal to the production fluid. Accordingly, numerous stuffing boxes for use with PCP implementations are available in the marketplace. Typically, the stuffing boxes are of the bottom mount variety. As the term “bottom mount” implies, the stuffing boxes are placed below the hydraulic motor and other components of the drive system. In many cases, the stuffing box is located beneath the drive system and directly above the wellhead.
The harsh operating environment of a PCP implementation necessitates regular servicing of stuffing boxes due to failed bearings and seals within. Servicing or replacing stuffing boxes prove to be difficult in the case of bottom mount stuffing boxes because they are difficult to gain access to. This is mainly because the drive system needs to be disconnected from the wellhead in order to remove the stuffing box.
There are some top mount stuffing boxes available in the marketplace, but they utilize rope packings as the primary seals. Those skilled in the art will understand that under rigorous conditions, rope type packings have a tendency to lose shape, or “weep”, which renders these packings ineffective for containing pressurized production fluids. Further, available top mounted stuffing boxes tend to damage other components of the drive system, such as a drive unit.
Therefore, there is a need for a top mounted stuffing box that allows for quick installation or removal without requiring the removal of other components of the drive system, such as the hydraulic motor or the drive unit. There is a further need for the stuffing box to contain seals that are more reliable and wear resistant than those known in existing stuffing boxes known in the art. There is yet a further need for the stuffing box to mate with other components of the drive system in a manner that will not damage these components.